invalidate-section

Arguments:
row-section column-section &optional redraw-now-p

Tells the operating system to invalidate the grid section specified by
the arguments so that the operating system will tell the grid section
to redraw itself after all other message processing has completed, or
immediately if redraw-now-p is true.

row-section may be either a row-section or
a grid-row, and
column-section may be either a
column-section or a grid-column. So you could, for example,
invalidate the area where a single grid-row crosses a whole
column-section.